The present invention relates to a freezing apparatus and more particularly to an improvement in a freezing apparatus for continuously freezing products that are to be frozen.
Hitherto an apparatus of this kind has been publicly known wherein as shown in FIG. 1 of the attached drawings an endless steel belt 1 made of stainless steel sheet and having a smooth surface is adapted to be driven substantially horizontally by a drive pulley 3 which is provided at the product extraction side 11 and adapted to be driven by a variable speed motor (not shown), the moving speed of steel belt 1 being controlled by the speed control of the variable speed motor so that the freezing time can be adequately regulated. In FIG. 1 the reference numeral 2 is a tension pulley to give steel belt 1 a predetermined tension, provided at the supply side 10 of the products. Disposed below steel belt 1 is a brine tank 4 in abutting relationship therewith, and the products that are to be frozen are adapted to be disposed on the upper surface of steel belt 1. Further, disposed above steel belt 1 is an air blast device comprising cooling coil fins 6 and a fan 7, both enclosed by a ventilating duct 8 so as to form an air circulation passage. The freezing zone 12 thus constituted is contained within an insulating tunnel 9 so as to prevent outside heat from invading freezing zone 12. Brine tank 4 is adapted so that cold brine 13 supplied from a cold brine inlet 14 and discharged from a cold brine exit 15 is recirculated therein, brine 13 being adapted to be cooled by a refrigerator separately installed (not shown). Cooling coil fins 6 are similarly adapted to have a refrigerant circulated therein through a refrigerant inlet 16 and outlet 17, the refrigerant being adapted to be cooled by another refrigerator installed outside.
The operation of the conventional apparatus explained above is as follows:
Upon supply of the products-to-be-frozen on steel belt 1 from product supply side 10, they enter freezing zone 12 along with belt 1 which is continuously travelling at a speed from product supply side 10 to product extraction side 11. During the movement together with belt 1 the products-to-be-frozen 5 are frozen through contact with steel belt 1 which is cooled by the brine 13 contained within brine tank 14 so as to be in contact with the under surface of belt 1. As to the upper surfaces of the products-to-be-frozen 5, they are frozen by an air blast issuing from an ventilating duct 8 within which the air is circulated to be cooled by cooling fin coils 6 and fan 7, both disposed within insulating tunnel 9, whereby fin coils 6 are adapted to be supplied with the refrigerant from the refrigerator installed outside. The products-to-be-frozen 5 thus leave tunnel 9 as steel belt 1 moves to the product extraction side 11, and carried to the succeeding process.
Since the conventional apparatus has such a constitution and operation as above described, although the under surfaces of the products-to-be-frozen are quickly frozen through contact freezing with the steel belt 1, their upper surfaces are frozen slowly by the direct blowing of the cooled air, and simultaneously suffering drying weight loss, deteriorating the quality of the products.
Moreover, since in this conventional apparatus two refrigerating systems, i.e. one for the cooling of the brine and the other for the cooling of the air blast, two refrigerators are required, increasing both the initial and running cost of the equipment.
An apparatus for rapidly cooling food has been publicly known as disclosed in Japanese Laid-Open Patent Publication No. 95047/1979 in which after the upper surface of the products-to-be-frozen have been rapidly frozen by injecting liquified gas or spreading dry ice on the moving products the under surface of the products are subsequently rapidly frozen on a steel belt the under surface of which is cooled by a freezing element.
Also a freezing apparatus has been publicly known as disclosed in Japanese Patent Publication No. 5022/1970 in which at least one of the contact surfaces between a belt conveyor and a cooling vessel against which the belt conveyor contacts are formed with a thin film which contains a good heat conductive and lubricative substance so that the lubricability and heat conductivity between the belt conveyor and the cooling vessel are improved.
Further, Japanese Patent Publication No. 46818/1976 discloses a method for cooling packaged food which is characterized in that packaged food at high temperature is sprayed with a sterilization liquid such as hydrogen peroxide, etc. in the form of a mist or a shower, and subsequently the liquid adhered on the packaged product is vapourized by cooling it with forced air, whereby the packaged product is rapidly cooled.
However, none of the publicly known apparatuses or methods teach or suggest the use of a flexible belt conveyor for rapidly freezing food-to-be-frozen as disclosed in the present invention to be fully described below.